The present invention concerns a timepiece movement with a tourbillon, fitted with a shock protection device. The present invention also concerns a watch fitted with this type of timepiece movement.
Tourbillon movements are mechanical devices for improving the accuracy of mechanical watches by offsetting interference with the isochronism of the balance due to the Earth's gravity. In order to do this, the regulating member that includes the balance and the escapement are mounted in a carriage, which is set in rotation, generally at the rate of one complete revolution per minute.
The tourbillon carriage is generally held in place between two pivots, respectively provided in the bottom plate of the movement and in a bridge of the movement. Alternatively, the carriage can pivot in a ball bearing, which makes it more visible from the dial side.
When it pivots between the bottom plate and a bridge, the carriage is generally formed of a bottom bridge, to which pillars carrying a top bridge are fixed, and these top and bottom bridges carry pivots which respectively rotate in a jewel carried by the bottom plate and a jewel carried by the movement bridge.
Depending upon the embodiment, the movement bridge can be formed either by an overhanging beam, or a beam that is embedded at both ends.
One drawback of these tourbillon mechanisms is their high sensitivity to shocks. Indeed, it is difficult to make a mechanism this type of resistant to accelerations of more than 3500 G without damage, while NIHS standards require resistance to accelerations of 5000 G.
In fact, if significant shocks are applied to the watch, the weight of the tourbillon carriage is such that the movement bridge bends or is deformed so that the carriage moves along its axis of rotation and causes the bottom pivot of the carriage to leave its jewel housing. Depending upon the intensity of the shock and thus the amplitude of movement of the carriage, the pivot may not return to its housing, which abruptly stops the carriage, and therefore the movement, from rotating. After a shock of this type, intervention by a watchmaker is thus necessary in order to get the watch to work again. It should be noted that, in some cases, the movement of the carriage may be such that the escape pinion is released from the toothing of the fixed second wheel, causing the barrel to be let down abruptly, which may lead to the destruction of some parts of the mechanism. This drawback is more significant in the case of a top bridge formed of an overhanging beam which has greater flexibility.
Various attempts have been envisaged to overcome this problem, such as making the carriage lighter, making the movement bridge more rigid, particularly by increasing the dimensions thereof, or even lengthening the bottom pivot of the carriage. However, these measures have not been able to provide satisfactory results without making the design more complex, and in doing so, affecting the attractiveness of the watches fitted with these mechanisms.
It is an object of the present invention to overcome the aforementioned drawbacks, in addition to others, by providing a timepiece movement with a tourbillon that has improved shock resistance compared to tourbillons of the prior art.
It is also an object of the invention to provide a timepiece movement of this type, which is has a simple, economical design and is easy to implement.
It is also an object of the invention to provide a timepiece movement of this type without affecting its usual attractive appearance.